The present invention relates to a jointed structure comprising at least two kinds of oxide superconductor having different melting points.
In recent years, oxide superconducting materials have drawn attention for their high critical temperatures, and their applications in such fields as electric power, NMR apparatus, magnetic shielding and the like are expected.
Measurement of very weak biomagnetism has become possible by using an oxide superconducting material and a simple cooling apparatus utilizing liquid nitrogen. Accordingly, further application of oxide superconducting material is expected in medical science and medical care, in particular.
In measurement of biomagnetism, the apparatus used therefor must be able to not only contain a living body but also form a space of very low magnetic field. As the container for living body, cylindrical structures have been proposed generally. In order for a cylindrical structure to form a space of very low magnetic field, it is necessary that a supercurrent strong enough to shield geomagnetism flow uniformly throughout the all parts of the cylinder. Accordingly, it has hitherto been thought that the cylinder for containing a living body must be produced in one piece. In production of oxide superconductor structures of large to small sizes, however, it is difficult to effect molding and firing always in one piece.
A cylinder used as a container for measurement of biomagnetism must have a minimum diameter of about 1 m and a length of about 3 m when the cylinder is used for, for example, a living body.
In producing such a large cylinder in one piece, a large electric furnace is required (this is not practical) and moreover it is thought to be extremely difficult with the present technique to obtain an oxide superconductor cylinder having uniform properties throughout the cylinder.
Hence, it becomes necessary in production of various oxide superconductor structures to prepare divided parts and then joint these parts.
Currently, in jointing oxide superconductor parts, it is known to use, as a jointing layer, an oxide superconducting material having the same composition as the oxide superconductor parts to be jointed. It is also known to add a small amount of a non-superconducting material to said superconducting material in order to improve the adhesion between the jointing layer and the oxide superconductor parts to be jointed.